Operated Gas Sensor Research Articles

Highly Sensitive OFET Based Room Temperature Operated Gas Sensors Using Thieno[3,2-b]thiophene Extended Phthalocyanine Semiconductor

Over the past decades, organic field-effect transistor (OFET) gas sensors have maintained a rapid development. However, the majority of OFET gas sensors show insufficient detection capability towards oxidizing and hazardous...

Side charge propagation in simultaneous KPFM and transport measurement of humidity exposed graphene FET sensor

The surface diffusion (dissipation) of charge carriers enhanced by water molecules in solution-based biosensors and ambient operating gas sensors strongly influence their resistance response, sensitivity, and stability in time. Therefore, the information on the charge distribution at interfaces of conductive and insulating parts is essential for the operating sensors. This work presents the simultaneous measurement of the longitudinal macroscopic resistance response and local surface potential (SP) mapping by Kelvin probe force microscopy (KPFM) on a graphene Hall bar sensor. The results show the propagation of an electric charge from the main graphene channel onto the neighboring SiO2 surface. The charge propagation strongly increases with the relative humidity and can be controlled by a bottom-gate voltage used in most sensors based on a field effect transistor (FET) architecture. As proved by the longitudinal resistance measurements, the resulting side charge accumulation has a very small impact on the 2D resistivity of the graphene channel. It has been explained by an application of the Thomas-Fermi theory, proving an efficient screening of side accumulated charge potential caused by a redistribution of the charge inside the wide graphene channel. The combination of a transport resistance response and KPFM provides a deeper understanding of sensors/biosensors functionality and their design features than a simple resistance response usually observed.

ArtEMon: Artificial Intelligence and Internet of Things Powered Greenhouse Gas Sensing for Real-Time Emissions Monitoring.

Greenhouse gas (GHG) emissions reporting and sustainability are increasingly important for businesses around the world. Yet the lack of a single standardised method of measurement, when coupled with an inability to understand the true state of emissions in complex logistics activities, presents enormous barriers for businesses to understanding the extent of their emissions footprint. One of the traditional approaches to accurately capturing and monitoring gas emissions in logistics is through using gas sensors. However, connecting, maintaining, and operating gas sensors on moving vehicles in different road and weather conditions is a large and costly challenge. This paper presents the development and evaluation of a reliable and accurate sensing technique for GHG emissions collection (or monitoring) in real-time, employing the Internet of Things (IoT) and Artificial Intelligence (AI) to eliminate or reduce the usage of gas sensors, using reliable and cost-effective solutions.

The influence of advanced materials on the analytical performance of semiconductor-based gas sensors.

Chemiresistive gas sensors are metal oxide-based sensors that have received significant attention in different fields. Ambient gas sensors are especially important in the fabrication of wearable probes for the real-time detection of biomarkers in human body samples. Usually, room temperature sensors are affordable due to their low power consumption, resulting in simple instrumentation and maintenance. To fabricate versatile gas sensors, i.e. sensitive, selective, ambient temperature operating gas sensors, and improve the sensing performance of the traditionally used sensor, new materials play an important role. In other words, new advanced materials are essential for designing and fabricating new gas sensors. Hence, in this review, the application and impact of new advanced materials in the fabrication of reliable gas sensors are discussed in detail. Special emphasis is given to the effect of new materials in the fabrication of room-temperature operating systems. Finally, future research outlook and possible challenges that may be encountered by reliable gas sensors are also explained.

Exploring optical and electrical gas detection based on zinc-tetra-phenyl-porphyrin sensitizer.

We developed optical waveguide (OWG), ultraviolet-visible spectrophotometry (UV-vis), and electrically operated gas sensors utilizing zinc-tetra-phenyl-porphyrin (ZnTPP) as sensitizer. Strikingly, ZnTPP thin-film/K+-exchanged glass OWG sensing element exhibits a superior signal-to-noise ratio of 109.6 upon 1ppm NO2 gas injection, which is 29.5 and 3.8 times larger than that of UV-vis (absorbance at wavelength of 438nm) and ZnTPP electrical sensing elements prepared on an alumina ceramic tube, respectively. Further results on Fourier infrared spectra and UV-vis spectra, confirm a strong chemical adsorption of NO2 gas on ZnTPP. Therefore, our studies highlight the selection of suitable detection technique for analyte sensing with ZnTPP.

2D–2D lattice engineering route for intimately coupled nanohybrids of layered double hydroxide and potassium hexaniobate: Chemiresistive SO2 sensor

2D–2D lattice engineering route is used to synthesize intimately coupled nanohybrids of layered double hydroxide (LDH) and potassium hexaniobate. The 2D–2D lattice engineering route is based on the electrostatically derived self-assembly of delaminated zinc-chromium-layered double hydroxide (ZC-LDH) nanosheets and potassium hexaniobate (HNb) nanosheets (ZCNb nanohybrids). The 2D–2D lattice-engineered ZCNb nanohybrids display expanded surface area, mesoporous anchored nanosheets network morphology, and intimate coupling between nanosheets. The 2D–2D lattice engineered ZCNb nanohybrids are used for the low temperature operated gas sensor. The ZCNb nanohybrids display outstanding selectivity for the SO2, with the high response of 61.5% compared to pristine ZC-LDH (28.08%) and potassium niobate (8%) at 150 °C. Moreover, ZCNb sensors demonstrate superior response and recovery periods of 6 and 167 s at 150 °C, respectively. This result underscores the exceptional functionality of the ZCNb nanohybrids as efficient SO2 sensors. Moreover, these findings vividly demonstrate that the 2D–2D lattice-engineered ZCNb nanohybrids are quite effective not only in improving the gas sensor activity but also in developing of new type of intimately coupled mesoporous LDH-metal-oxide based hybrid materials.

Room temperature SO2 and H2 gas sensing using hydrothermally grown GO–ZnO nanorod composite films

Graphene based 2D materials with a surfeit of active sites and advantageously high surface to volume ratio are effectively linked to well established nanostructured semiconducting metal oxides for development of nanocomposites with enhanced gas sensing properties. Graphene Oxide (GO), a sister material of graphene, is therefore a natural choice for development of room temperature operated gas sensors. In the current investigation hydrothermally grown GO and ZnO nanorods composite (GO–ZnO–NR) is utilised for room temperature gas sensing of H2 and SO2 gases. Room temperature detection of H2 and SO2 at sub-100 ppm levels with linear variation in response for different concentrations is demonstrated. Morphological and structural analyses are conducted using Scanning electron microscopy, Raman spectroscopy and X-ray diffraction. GO-ZnO-NR composite sensor is seen to exhibit robust sensing response of 5.82 and 5.45 for 100 ppm each of H2 and SO2 gases respectively at room temperature. Further, the delayed response and recovery times exhibited by the sensor for SO2 gas are recognized to be due to formation of strongly adhering SO3 species.

Long Range Surface Plasmons assisted highly sensitive and room temperature operated NO2 gas sensor

Long Range Surface Plasmons (LRSPs) are excited in the SnO2/Au/SnO2/prism structure using Kretschmann configuration for detecting NO2 gas. SnO2 thin films of two different thicknesses are grown by RF sputtering technique and 205 nm thin SnO2 film resulted in the sharp LRSP resonance (LRSPR) reflectance curve with the minimum reflectance (Rmin) = 0.05 at the resonance angle (θspr) of 42.38°. LRSPR based room temperature (22 °C) operated gas sensor using the optimized SnO2/Au/SnO2/prism configuration is developed in the present work for effectively detecting NO2 gas in a broad concentration range from 0.5 ppm to 2000 ppm. The LRSPR reflectance curve corresponding to the prepared sensor shows an appreciable shift of 8.47° in the resonance angle on exposure to NO2 gas (2000 ppm). The developed optical sensor illustrated high sensitivity (0.2°/ppm) along with the limit of detection (LOD) of 0.38 ppm of NO2 gas. The sensor exhibited outstanding selectivity towards NO2 gas and showed insignificant response to various other interfering gases. The obtained results highlight the successful fabrication of competent LRSPR based optical gas sensor capable of detecting NO2 gas at room temperature.

Polymer/Graphene oxide nanocomposite thin film for NO2 sensor: An in situ investigation of electronic, morphological, structural, and spectroscopic properties

The higher operating temperature of metal oxide and air instability of organic based NO2 sensor causes extremely urgent for development of a reliable low cost sensor to detect NO2 at room temperature. Therefore, we present a fabrication of large area Polymer/GO nano hybrid thin film for polymer thin film transistors (PTFTs) based NO2 sensors assisted via facile method named ‘spreading-solidifying (SS) method’, grown over air/liquid interface and successive investigation of effect of NO2 on film via several characterizations. The PTFTs sensor has demonstrated swift and high response towards low concentration of NO2 gas with air stability and provided real time non-invasive type NO2 sensor. Herein, we are reporting the nanohybrid PBTTT/GO composite based PTFT sensor with good repeatability and sensor response for low concentration NO2. The thin film grown via SS technique has reported very good adsorption/desorption of target analyte having response/recovery time of 75 s/523 s for 10 ppm concentration of NO2 gas. It has been observed that % change in drain current (sensor response) saturated with increasing concentration of NO2. The transient analysis demonstrates the fast sensor response and recovery time. Furthermore, in order to understand the insight of high performance of sensor, effect of NO2 on nanohybrid film and sensing mechanism, an in situ investigations was conducted via multiple technique viz. spectral, electronic, structural, and morphological characterization. Finally, the performance of sensor and the site of adsorption of NO2 at polymer chains were argued using schematic diagram. This work shows the simple fabrication process for mass production, low cost and room temperature operated gas sensors for monitoring the real-time environment conditions and gives an insight about the sensing mechanism adsorption site of NO2.

Facile control of room temperature nitrogen dioxide gas selectivity induced by copper oxide nanoplatelets

Development of room-temperature operating gas sensors, utilizing p-type CuO nanoplatelets for air quality monitoring with excellent response, high sensitivity and good reliability, is highly desirable. Therefore, in this work, we investigated both the influence of synthesis reaction temperature and time on the sensitivity, selectivity, and response of CuO nanoplatelets prepared through the hydrothermal synthetic method, in the presence of NaOH as base, without the support of any surfactant. The gas sensing findings revealed that the CuO nanoplatelets NO2 sensitivity and selectivity can be controlled and tuned by adjusting the synthesis reaction temperature and time, while maintaining the morphology. The CuO-based sensors revealed a remarkable response of 14.5 to 20 ppm NO2, with a sensitivity of 0.47 ppm−1 at room temperature. A decrease in sensing performance was observed at higher operating temperatures. The findings affirmed that such sensor response/sensitivity is not dependent on the specific surface area and is relatively interrelated to the adsorption sites, the average crystallite size, and low charge carrier concentration, giving rise to a more pronounced change in CuO sensor resistance. The influence of relative humidity (RH) was also investigated to have an understanding of the sensor performance in real testing conditions. Additionally, the stability analyses to four cycles of different humidity percentages and gas concentration-related repeatability conditions were carried out, and the sensor revealed a slight drifting when increasing the number of testing cycles.

Room temperature chemiresistive gas sensors: challenges and strategies—a mini review

One of the sources of environmental threat in recent years is the leakage of toxic gases from various industries. Sensors to detect these gases in trace level concentrations are highly required to ensure a safe living environment. In this context, many types of gas sensors such as calorimetric, conductometric, potentiometric, catalytic, and chemiresistive types have been employed to detect these gases. Among them, chemiresistive type sensors have been widely employed due to high selectivity, sensitivity, simplicity in fabrication, compactness, lower operating temperature, and low power consumption. Chemiresistive sensors are designed with inbuilt micro-heaters for improving the sensing response. However, sensors operated at elevated operating temperatures would significantly affect the stability of the sensor due to grain growth. To address this concern, many efforts have been progressing over the years towards the development of room temperature operated gas sensors. In this review, room temperature operated gas sensors developed for the detection of ammonia, acetaldehyde, ethanol, nitrogen dioxide, ozone, and aromatic VOCs have been discussed. In addition, the major challenges possessed by the sensors operated at elevated temperatures such as grain growth, change of conductivity, and variations in charge transport characteristics have been addressed. Also, the strategies to minimize the aforementioned challenges have been highlighted.

Metal-Organic Frameworks-Derived Hierarchical Co3O4 Structures as Efficient Sensing Materials for Acetone Detection.

Highly sensitive and stable gas sensors have attracted much attention because they are the key to innovations in the fields of environment, health, energy savings and security, etc. Sensing materials, which influence the practical sensing performance, are the crucial parts for gas sensors. Metal-organic frameworks (MOFs) are considered as alluring sensing materials for gas sensors because of the possession of high specific surface area, unique morphology, abundant metal sites, and functional linkers. Herein, four kinds of porous hierarchical Co3O4 structures have been selectively controlled by optimizing the thermal decomposition (temperature, rate, and atmosphere) using ZIF-67 as precursor that was obtained from coprecipitation method with the co-assistance of cobalt salt and 2-methylimidazole in the solution of methanol. These hierarchical Co3O4 structures, with controllable cross-linked channels, meso-/micropores, and adjustable surface area, are efficient catalytic materials for gas sensing. Benefits from structural advantages, core-shell, and porous core-shell Co3O4 exhibit enhanced sensing performance compared to those of porous popcorn and nanoparticle Co3O4 to acetone gas. These novel MOF-templated Co3O4 hierarchical structures are so fantastic that they can be expected to be efficient sensing materials for development of low-temperature operating gas sensors.

An Ultrasensitive Organic Semiconductor NO2 Sensor Based on Crystalline TIPS‐Pentacene Films

Organic semiconductor gas sensor is one of the promising candidates of room temperature operated gas sensors with high selectivity. However, for a long time the performance of organic semiconductor sensors, especially for the detection of oxidizing gases, is far behind that of the traditional metal oxide gas sensors. Although intensive attempts have been made to address the problem, the performance and the understanding of the sensing mechanism are still far from sufficient. Herein, an ultrasensitive organic semiconductor NO2 sensor based on 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-petacene) is reported. The device achieves a sensitivity over 1000%/ppm and fast response/recovery, together with a low limit of detection (LOD) of 20 ppb, all of which reach the level of metal oxide sensors. After a comprehensive analysis on the morphology and electrical properties of the organic films, it is revealed that the ultrahigh performance is largely related to the film charge transport ability, which was less concerned in the studies previously. And the combination of efficient charge transport and low original charge carrier concentration is demonstrated to be an effective access to obtain high performance organic semiconductor gas sensors.

Room temperature a.c. operating gas sensors based on quaternary chalcogenides

Impedance spectra of quaternary As–Ge–S–Te based alloys were investigated in both dry synthetic air and mixture with nitrogen dioxide in order to assess the use of these materials in future gas sensors working at room temperature (22°C). To elucidate the effect of tellurium, the quaternary compositions As2Te13Ge8S3 and As2Te130Ge8S3, with increasing concentration of Te have been considered along with pure tellurium films. Shown by AFM, SEM and X-ray analysis the nature of the films was predominantly amorphous but the morphology of the films grown on sintered alumina substrates appears to consist of interconnected islands and dots, which facilitate the solid–gas interaction. Analyses in Cole–Cole interpretation allowed evaluating the characteristic frequency, time constant, resistance and capacity of the films in both dry air and its mixture with NO2. It is shown that impedance spectra being strongly influenced by gaseous environment are also strongly influenced by material composition and phase-structural state of the film. Sensitivity spectra to nitrogen dioxide denote the competitive influence of carrier transport via states of allowed bands, hopping between localized states in the extended band tails or tunneling (variable range hopping) between localized states close to Fermi level. Impedance sensitivity being maximal for amorphous As2Te13Ge8S3 is assumed to be controlled by this competition of transport mechanisms.

Zinc Oxide Nanowire Based Hydrogen Sensor On SOI CMOS Platform

Here we report on the successful low-temperature growth of zinc oxide nanowires (ZnONWs) on silicon-on- insulator (SOI) CMOS micro-hotplates and their response, at different operating temperatures, to hydrogen in air. The SOI micro-hotplates were fabricated in a commercial CMOS foundry followed by a deep reactive ion etch (DRIE) in a MEMS foundry to form ultra-low power membranes. The micro-hotplates comprise p+silicon micro-heaters and interdigitated metal electrodes (measuring the change in resistance of the gas sensitive nanomaterial). The ZnONWs were grown as a post-CMOS process onto the hotplates using a CMOS friendly hydrothermal method. The ZnONWs showed a good response to 500 to 5000ppm of hydrogen in air. We believe that the integration of ZnONWs with a MEMS platform results in a low power, low cost, hydrogen sensor that would be suitable for handheld battery- operated gas sensors.

Platform for a Hydrocarbon Exhaust Gas Sensor Utilizing a Pumping Cell and a Conductometric Sensor

Very often, high-temperature operated gas sensors are cross-sensitive to oxygen and/or they cannot be operated in oxygen-deficient (rich) atmospheres. For instance, some metal oxides like Ga2O3 or doped SrTiO3 are excellent materials for conductometric hydrocarbon detection in the rough atmosphere of automotive exhausts, but have to be operated preferably at a constant oxygen concentration. We propose a modular sensor platform that combines a conductometric two-sensor-setup with an electrochemical pumping cell made of YSZ to establish a constant oxygen concentration in the ambient of the conductometric sensor film. In this paper, the platform is introduced, the two-sensor-setup is integrated into this new design, and sensing performance is characterized. Such a platform can be used for other sensor principles as well.

Low power gas detection with FET sensors

The work function principle of gas sensing is dedicated for room or slightly elevated temperatures of operation as signal contributions from both physisorption and chemisorption will be detectable. Prerequisite are FET transistors either with permeable gates made of palladium or polymers or with a suspended gate whose air gap permits the access of gases to the inner surfaces of the gate capacitance. The later design allows to incorporate almost all groups of sensitive materials, if a hybrid construction is used. The available models for metal oxide and electrochemical sensors can be adopted for comprehension of this surface potential method and for an estimative overview for the development of new sensors. The presented results show the vast capability of the work function principle leading to micro gas sensors with low power consumption suitable for low cost applications. Nevertheless, the general requirements for well operating gas sensors — high selectivity, high sensitivity, high stability and high S/N ratio — can be satisfied.